Field of the Invention
The present invention relates to a sheet processing apparatus configured to perform folding processing on a sheet or a bundle of sheets delivered from an image forming apparatus, and further relates to an image forming system including the sheet processing apparatus.
Description of the Related Art
Hitherto, there has been provided a sheet processing apparatus configured to perform folding processing on a bundle of sheets to form a booklet, as post-processing for a sheet delivered from image forming apparatus such as a copying machine, a printer, a facsimile, and a multifunctional peripheral of those devices. For example, there has been known a sheet post-processing apparatus configured to sequentially perform folding processing using a crease forming portion with respect to sheets conveyed from a copying machine main body through a conveyance path to form creases on the sheets, and thereafter return the sheets to the conveyance path and stack the sheets on a stacking tray so that the creases overlap with each other (Japanese Patent Application Laid-Open No. 2003-276943).
In the sheet post-processing apparatus, the crease forming portion includes a horizontal conveyance path defined by a pair of upper and lower guide plates, and a folding roller pair disposed so as to face the conveyance path through a gap (processing region) formed between the lower guide plates. On an outer circumference of each folding roller, there are formed a guide portion and a folding portion. The guide portion has a flat surface with a small friction coefficient and is configured to guide a sheet. The folding portion has a circular circumferential surface with a large friction coefficient and is configured to fold a sheet. The sheet is conveyed in the conveyance path in a state in which the guide portions of the folding rollers are opposed to the conveyance path.
According to the conventional apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-276943, the guide portions of the folding roller pair, which is a pair of rotary members, are configured to directly guide the sheet on the conveyance path. With the folding roller pair, there is formed a relatively small gap between the folding portions and the conveyance path, whereas there is formed a relatively large gap between the guide portions and the conveyance path. Therefore, a leading edge of the sheet may enter a gap between the guide portion of the folding roller pair and the lower guide plate, or may be caught by the guide portion. Thus, there is a fear of causing sheet jamming.